I am trying to calculate maximum junction capacitance (or depletion capacitance) \$C_j\$ for the BAT62-02L diode from this datasheet based on its SPICE parameters:

  • \$I_s=\$ IS \$=\$ Saturation current \$=250~\text{nA}\$.
  • \$\eta=\$ XN \$=\$ N \$=\$ Emission coefficient \$=1.04\$.
  • \$r_s=\$ RS \$=\$ Series resistance \$=190~\Omega\$.
  • \$C_{j0}=\$ CJ0 \$=\$ Zero-bias junction capacitance \$=284.2~\text{fF}\$.
  • \$\phi=\$ PB \$=\$ VJ \$=\$ PN junction potential \$=0.224~\text{V}\$.
  • \$m=\$ MJ \$=\$ M \$=\$ PN grading coefficient \$=0.17\$.
  • \$\tau=\$ TT \$=\$ Transit time \$=55~\text{ps}\$.
  • \$V_{br}=\$ BV \$=\$ Reverse breakdown voltage \$=42~\text{V}\$.
  • \$E_g=\$ EG \$=\$ Band-gap voltage \$=0.53~\text{eV}\$.
  • \$p=\$ XTI \$=\$ IS temperature exponent \$=1.5\$.

I found this in c11 of MOSFET Models for VLSI Circuit Simulation:


But he says that this only holds for \$V_d\leq\frac{\phi}{2}\$... Another source gives the following:

$$C_j = \cases{\frac{C_{j0}}{\left(1-\frac{V_d}{\phi}\right)^m}, & $V_d\leq \text{FC}\cdot\phi$\\ \frac{C_{j0}\left(1-\text{FC}(m+1)+\frac{mV_d}{\phi}\right)}{\left(1-\text{FC}\right)^{(m+1)}}, & $V_d>\text{FC}\cdot\phi$}$$

Is this correct & am I wrong to assume that \$\text{FC}\$ (the Forward-bias depletion capacitance coefficient) is always 0.5?


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